A. E. Yerrill — Study of the family Pectinidce. 59 



numerous interpolated ribs, increasing in number with age. The 

 ribs are generally crossed by concentric sculpture, often forming- 

 rough scale-like projections. The margins are scalloped and the 

 shell closes rather tightly except at the bj^ssal area. The inner sur- 

 face has ribs and double flutings, corresponding to the external 

 grooves and radii. The hinge-plate generally has two slightly 

 divergent ribs on each end. For some account of the anatomy of 

 C. Islandica, see p. 72. Some of the species are known to have sep- 

 arate sexes. 



The genus is world-wide in distribution. It appeai-ed early in 

 mesozoic geological time (Triassic) and is common in Cretaceous and 

 Tertiary rocks. 



Among the American species of Chlamys are the following, be- 

 longing to the tyjHcal or restricted group : C. Islandica Linne, from 

 the northern coasts and fishing banks ; C. ornata (L.), from the 

 southern coasts of the United States and the West Indies ; C exas- 

 2)erata (Sow.), West Indies; C. costellata Verrill and Bush, from 

 deep water ; C. JSenedicti V. and B., from deep water off the east- 

 ern coast of the United States and in the West Indies ; C. phrygia 

 (Dall), Gulf of Mexico and West Indies, 95-127 fath ; C. effluens 

 (Dall), 127 fath., off Havana. Several of the common American 

 species belong to the subgenus uEquipecten (see p. 67). Among 

 them are G. irradians, C. dislocata, C Antillarum, C. glypta (pi. 

 xvi, figs. 7-11), and C. ventricosa. 



Pallium. Schumacher. Type, P. plica (Linne). 



Pallium Schumacher, 1817; H. and A. Adams, 1858; Chenu, 1862; Stoliczka, 

 1871; Zittel, 1881; Fischer, 1887. 



Dentipecten Ruppel, 1835. 



Plate XXL fig. 4. 



The special feature of this very distinct group is the development 

 of several (usually three) well-marked, nearly transverse, blunt 

 teeth, alternating with distinct pits, on each end of the hinge-plate. 

 The shell is elevated, rather thick, with external, large, obtuse or 

 rounded, radial ribs or corrugations and with internal, angular, dou- 

 ble or bicarinate ribs, opposite the external grooves, near the margin. 

 The auricles are small, but high. The hinge-teeth are marked with 

 distinct cross lines. 



Hinnites Def ranee, 1821. Type, H. Cortessi Def. 



Shell free and much like Chlamys, when young, but later \\\ life it 

 becomes attached by the right valve and irregular. Mr. Dall. has 



